The background of the present invention is described hereinbelow:
(1) Random access of an LTE (Long Term Evolution) system. The reasons that a random access may be triggered by the LTE system include: initial access; handover caused by RRC (Radio Resource Control) connection reestablishment and mobility; downlink (DL) data arrival while uplink (UL) loss in RRC connected status; in RRC connected status, UL data arrival while DL loss or no D-SR (dedicated scheduling request) resources or the maximum number of D-SR transmissions having been reached; intra-cell handover due to security reasons; and positioning, etc.
For the intra-cell handover caused due to DL data arrival, mobility handover and security reasons, if a dedicated preamble (Random Access Preamble) is available, a non-contention based random access may be selected. FIG. 1 shows a schematic diagram of the non-contention based random access, including:
Msg0: a base station allocates a dedicated ra-PreambleIndex for non-contention based random access and a PRACH (Packet Random Access Channel) resources for random access, that is, ra-PRACH-MaskIndex (PRACH Mask Index) to the UE (User Equipment).
For a non-contention based random access caused by the DL data arrival, the message is passed by use of PDCCH (Physical Downlink Control Channel); while for a non-contention based random access caused by the handover, the message is passed via the handover command.
Msg1: the UE sends an appointed dedicated preamble to the base station through the designated PRACH resources according to the ra-PreambleIndex and ra-PRACH-MaskIndex instructed by the Msg0. After receiving the Msg1, the base station calculates the UL TA (Timing Alignment) according to the Msg1.
Mgs2: the base station sends a random access response (RAR) message to the UE, the RAR contains the TA information, informing the UE of the TA of the follow-up UL transmission.
For the random accesses caused by other reasons, the contention-based random access may be adopted, as shown in FIG. 2. In the LTE system, the basic mechanism of the contention-based random access is shown as follows: in a plurality of preambles available, the terminal randomly selects a preamble, and sends it through an RACH (Random Access Channel); after receiving the preamble, the network calculates the deviation between the actual arrival time and expected arrival time of the preamble, and then marks the deviation as a TA and sends it to the terminal through an RAR message. After receiving the TV, the terminal may establish a UL synchronism with the network by adjusting the sending time of the UL message with the TA. Upon completion of TA, the terminal also needs to send its unique ID to the network side in order to eliminate the collision.
FIG. 2 is the process diagram of the contention-based random access solution in the LTE system.
Msg1: the terminal randomly selects a preamble among all preambles available and sends the preamble through an RACH. When the terminal sends the preamble, the base station also detects the RACH, and calculates the corresponding TA of the preamble if the preamble is detected.
Msg2: the base station sends an RAR message of the preamble detected, which contains the following information: (1) identity information of the preamble received, such as serial number and sending time; (2) corresponding TA of the preamble received; (3) information on channel resources allocated for the subsequent UL data transmission, including the frequency-time position of resources and MCS (modulation and coding style), etc., and (4) a temporary ID allocated for users by the base station (such as C-RNTI).
Furthermore, after receiving the RAR message, the terminal determines whether the target terminal of the RAR message is the terminal itself by using the identity information of the preamble in the RAR message, and if yes, adjusts the sending TA of the UL signals according to the TA information in the RAR message.
Msg3: the terminal sends the UL data. The UL resources used by the UL data are those allocated for the terminal by the base station in the Msg2. The UL data sent by the terminal includes at least: identity information of the terminal, such as IMSI (International Mobile Subscriber Identity), TMSI (Temporary Mobile Subscriber Identity), or C-RNTI (Cell Radio Network Temporary Identity).
Msg4: the base station detects whether the terminal identity information sent in the Msg3 by the terminal is legal, and notifies the terminal of the detection results by sending a contention resolution message.
After completing the aforesaid procedure of random access, the terminal and the base station may realize the UL data transmission.
(2) Network structure of an LTE-A (LTE-Advanced) system: FIG. 3 shows a network structure diagram of the LTE-A system.
a. An eNB (Evolved Node B) is connected to a core network (CN) through a wired interface.
b. The RN (Relay Node) is connected to the eNB through a radio interface which is called Un interface. The corresponding radio link is called backhaul link (BH link), and the eNB connected with the RN is called donor eNB (DeNB) of the RN.
c. The UE is connected to the RN or eNB through a radio interface which is called Uu interface. The corresponding radio link is called access link (AC link), the UE directly connected with the eNB is called Marco UE, and the UE directly connected with the RN is called R-UE.
(3) Design of BH Link
The introduction of an RN provides three radio links in the RN-based mobile communication system, namely, an access link between the DeNB and the Marco UE (Marco UE AC link), a backhaul link between the DeNB and the RN (BH link), and an access link between the RN and the R-UE (R-UE AC link).
Specifically, as the RN is an in-bank relay node, that is, interference occurs if the RN sends/receives data to/from the R-UE when sending/receiving DeNB signals, the BH link and the R-UE AC link can't co-exist simultaneously in order to avoid the self interference. However, the Marco UE AC link and the BH link can coexist, provided that the time-frequency resources of the two are orthogonal.
A method for coordinating the BH link and the R-UE AC link is to build “gaps” within the DL access transmission time of the R-UE at the Uu interface, wherein, the gaps are used for the DL BH link, and the configuration of the gaps may be realized by using an MBSFN (Multicast Broadcast Single Frequency Network) subframe.
FIG. 4 shows a schematic diagram of the DL link transmission by using an MBSFN subframe. The DeNB and the RN realizes the DL transmission among these gaps, while there is no DL transmission between the RN and the R-UE.
In addition, the UL BH subframe is corresponding to the DL BH subframe, and the UL BH subframe may be instructed in an explicit or implicit way. Similarly, to avoid the self interference of the RN, the UL BH subframe on the BH link can only be used for the UL transmission between the RN and the DeNB, and the R-UE is limited to the UL transmission on the Uu interface or between the RNs.
(4) RN status of the LET-A system: the start-up procedure of an RN in the LET-A system includes the following steps: 1) building a synchronism with the DeNB and a connection with the RRC through an random access procedure; 2) being attached to the network through the Attach procedure; 3) downloading the configuration information from a Q&M system; and 4) building the S1 and X2 interfaces.
For the aforesaid step 1) and 2), the RN works according to the UE mode. After completing the step 4), the RN works as a base station. If working in UE mode, the RN may use all resources of the system without limitation by the BH subframe; if working in the base station mode, the RN may perform the data transmission of the Un interface only by using the UL/DL BH subframe.
(5) Random access of an RN: in the LTE-A system, no matter whether the RN works in UE mode or base station mode, the random access procedure is not avoided.
Specifically, if an RN works in UE mode, the reason that a random access may be triggered include: initial access; if the RN works in base station status, the reason that a random access may be triggered include: RRC connection reestablishment of the RN, such as failure of radio link at the Un interface; DL data arrival but UL loss in RRC connected status; in RRC connected status, UL data arrival while DL loss or no D-SR resources or the maximum number of D-SR transmissions having been reached; intra-cell handover caused due to security reason.
In the process of realizing the objects of the present invention, at least the following problems existing in the prior art were found: during the startup of the RN, if working in UE mode, the RN may use all subframe resources for the BH-subframes are not available in this case, and the random access of the RN startup is consistent with that of the ordinary UE. However, if working in base station mode, the RN working as a base station can only use the BH link resources of the Un interface if any random access is triggered, and the limitation of BH subframes will result in the time delay for performing the random access of the RN, and influence the R-UE user experience.